Vaccines:safety of non-active substancesIt is important to monitor continuously the safety of all different substances of vaccines, in order to ensure the safety of vaccination campaigns. Non-active substances, such as adjuvants and antiseptics, are ultimately together with the antigens responsible for the safety and the immunogenicity of vaccines.For decades aluminium has been used to increase the immunogenicity of vaccines. In the nineties however, it has been surmized that the use of aluminum in vaccines could play an etiological role in a newly discovered myopathy: macrofagic myofasciitis. However, no connection between the use of aluminium in vaccines and neurological disorders has been proven.Thiomersal is a mercury containing antiseptic, which has been safely used in vaccines since 1930. In 1999, the use of thiomersal in vaccines has been suggested to be responsible for certain neurological developmental disorders in small children. At this moment no link, what so ever, has been demonstrated.Still and following the principle of "extreme caution" in order to support the safety of vaccination, it has been decided to adapt the production methods and to remove progressively thiomersal from vaccines.